The long term goal of this research is a better understanding of the processes which lead to bone resorption and accretion in vivo. At present much of the work deals with the role of bone blood flow in the regulation of skeletal metabolism. Specific aims include: (a) To study if short term changes in bone blood flow cause alterations in calcium and phosphate release from bone. (b) To investigate the role of bone blood flow in long term bone resorption and accretion. (c) To elucidate the mechanisms which regulate skeletal blood flow. (d) To determine if calcitonin alters the vasoactive effects of PTH on bone.